Rapid Assembly of Saturated Nitrogen Heterocycles in One‐Pot: Diazo‐Heterocycle “Stitching” by N–H Insertion and Cyclization

Methods that provide rapid access to new heterocyclic structures in biologically relevant chemical space provide important opportunities in drug discovery. Here, a strategy is described for the preparation of 2,2‐disubstituted azetidines, pyrrolidines, piperidines, and azepanes bearing ester and diverse aryl substituents. A one‐pot rhodium catalyzed N–H insertion and cyclization sequence uses diazo compounds to stitch together linear 1,m‐haloamines (m=2–5) to rapidly assemble 4 ‐, 5 ‐, 6 ‐, and 7 ‐membered saturated nitrogen heterocycles in excellent yields. Over fifty examples are demonstrated, including examples with diazo compounds derived from biologically active compounds. The products can be functionalized to afford α,α‐disubstituted amino acids and applied to fragment synthesis.     

A continuous flow system design for simultaneous determination of heavy metals in river water samples

A new design of a continuous flow system applied to the simultaneous determination of the concentration of zinc(II), cadmium(II), lead(II), copper(II), nickel(II), cobalt(II) and chromium(VI) in river water is described. A flow cell made in the laboratory, which has been patented, based on a 'wall-jet' configuration with a three-electrode system is described. Optimum conditions for the determination of the metal ions are reported. The detection limits and relative standard deviation values were 4.01x10(-9) M and 0.078 for Zn(II), 1.76x10(-10) M and 0.056 for Cd(II), 4.69x10(-10) M and 0.134 for Pb(II), 2.29x10(-10) M and 0.138 for Cu(II), 1.61x10(-9) M and 0.093 for Ni(II), 1.91x10(-9) M and 0.113 for Co(II), and 1.35x10(-9) M and 0.081 for Cr(VI). The procedure was applied to a sample of water from the Arlanzón river and the results were compared with inductively coupled mass plasma spectrometry (ICP-MS) as reference method. The final aim of this work is to design a flow system, which can be automated.     

Correlation between Solution and the Solid State: The pH Dependent Composition in the Ternary System [Co(H2O)6]2+ or [Ni(H2O)6]2+/Piperazine/Phosphate

The protolytic equilibria of piperazine (C₄H₁₀N₂) and phosphate have been investigated in the presence of cobalt or nickel chloride or nitrate by potentiometric titrations between pH 2 and 8. Potentiometric titrations suggest the presence of [M²⁺(H₂O)₅(C₄H₁₁N₂⁺)]³⁺ and [M²⁺(H₂O)₅(C₄H₁₀N₂)]²⁺ in solution with stability constants logK of 3.1 and 3.8 for M = Co and 3.1 and 3.6 for M = Ni, respectively. Crystallization experiments were then conducted at selected pH values to isolate desired species from the known solution composition. Crystallization afforded [M(H₂O)₆]²⁺(C₄H₁₂N₂²⁺)(HPO₄^2—)₂ at pH 3.5 and 6.2 (M = Co, Ni), and Co₃(PO₄)₂·8H₂O at pH 10.5. No crystals with the dihydrogenphosphate anion or a metal‐bound piperazine ligand could be isolated under the reaction conditions. The solid‐state assembly in the isomorphous structures of [M(H₂O)₆](C₄H₁₂N₂)(HPO₄)₂ with M = Co and Ni is based on an extended hydrogen bonded network between the three ionic building blocks.     

(C6H14N2)2[VO(HPO4)5B2O]·H2O·H3PO4, a novel borophosphate cluster containing a single vanadium centre and linked by hydrogen bonds into a three‐dimensional framework

The title novel vanadium borophosphate compound, bis(1,4‐diazo­nia­[2.2.2]­octane) μ₃‐oxo‐oxopenta‐μ‐phosphato‐diboronvanadium monohydrate phosphoric acid solvate, containing the cluster anion [VO(PO₃OH)₅B₂O]⁴⁻, has been synthesized under mild hydro­thermal conditions. Extensive O—H⃛O and N—H⃛O hydrogen bonding is observed between the molecular units.     

Steric interactions mediated by multiblock polymers and biopolymers: role of block size and addition of hydrophilic side chains

To a first approximation, the primary structure of many food proteins maybe thought of as a sequence of short hydrophobic and hydrophilic blocks. The influence of this type of structure on the steric-stabilising properties of such proteins has been considered here. In line with previous studies, using Self-Consistent-Field calculations, it has been shown that the presence of such protein molecules can lead to attraction and consequently bridging flocculation of colloidal particles. In the low adsorption energy limit for the hydrophobic groups (−1k_BT), it is found that the steric potential is significantly influenced by the changes in the number of adsorbed segments, as two surfaces are brought together. This is in contrast to the well-known results in the literature for the high adsorption limiting cases, where the number of such segments remains constant. In particular, the changes in the number of adsorbed hydrophobic units are observed not to be a monotonic function of the separation distance, but increase or decrease in reasonable accord with the oscillatory nature of the steric interactions, observed for various block sizes. Effects of the addition of a moderately sized hydrophilic side chain to the above molecules have also been studied. It is found that, in principle, such a modification can lead to a purely repulsive steric potential in solutions of these hybrid biopolymers. At the hydrophilic side chain sizes considered here, the surface affinity of the molecules is observed not to be drastically different compared to those of unmodified proteins.     

Crystal structures and physico-chemical properties of Zn(II) and Co(II) tetraaqua(3-nitro-4-hydroxybenzoato) complexes: Their anticonvulsant activities as well as related (5-nitrosalicylato)–metal complexes

Purposes of these studies were to synthesize Zn(II) and Co(II) complexes of 3-nitro-4-hydroxybenzoic acid, determine their structures through X-ray crystallography, and obtain their anticonvulsant activities. Thermogravimetric, differential scanning calorimetry, impedance of aqueous solutions and magnetic properties analyses were also determined. Anticonvulsant and related activities of these complexes as well as Zn(II), Co(II), Ni(II) and Mg(II) (5-nitrosalicylato) complexes were determined by the National Institutes of Health, Antiepileptic Development Program. Results of these analyses are presented to document unique bonding features and physical properties of these compounds and their anticonvulsant activities. It is concluded that these compounds have chemical and physical properties that can be used to account for their anticonvulsant activities.     

Multisegmented one-dimensional nanorods prepared by hard-template synthetic methods

In the science and engineering communities, the nanoscience revolution is intensifying. As many types of nanomaterials are becoming more reliably synthesized, they are being used for novel applications in all branches of nanoscience and nanotechnology. Since it is sometimes desirable for single nanomaterials to perform multiple functions simultaneously, multicomponent nanomaterials, such as core-shell, alloyed, and striped nanoparticles, are being more extensively researched. Nanoscientists hope to design multicomponent nanostructures and exploit their inherent multiple functionalities for use in many novel applications. This review highlights recent advances in the synthesis of multisegmented one-dimensional nanorods and nanowires with metal, semiconductor, polymer, molecular, and even gapped components. It also discusses the applications of these multicomponent nanomaterials in magnetism, self-assembly, electronics, biology, catalysis, and optics. Particular emphasis is placed on the new materials and devices achievable using these multicomponent, rather than single-component, nanowire structures.     

Structure/property relationship of Schrock-type alkylidene complexes based on tungsten and molybdenum

The structure/property relationship of Schrock-type alkylidene complexes with tungsten and molybdenum as central atoms was investigated. Terminal and, E and Z internal olefins as well as double bond substituted and unsubstituted unsaturated polymers served as metathesis substrates. According to the results obtained, it is possible to choose the optimal catalyst depending on the metathesis substrate and temperature, the central atom plays a decisive role. Examples concerning equilibrium polymerization demonstrate the practical utilization.     

Polymer-assisted laser desorption/ionization analysis of small molecular weight compounds

The use of non-polar, small polymers as matrices for the analysis of low molecular weight compounds in polymer-assisted laser desorption/ionization mass spectrometry (PALDI-MS) is demonstrated. The matrices evaluated were either based on an oligothiophene or a benzodioxin backbone. Metallocenes, polycyclic hydrocarbons, a fluorosurfactant, and a subset of small organic compounds with various functionalities, served as model analytes. The mechanism of ionization charge transfer is discussed and ionization potentials for the matrices in the study have been estimated using density functional theory (DFT) calculations. Some of the results are possibly contradictory to the generally accepted limiting conditions for gas-phase charge-transfer reactions. These results are interpreted in the light of energy pooling. Also a new mass calibration procedure for the low-mass region in positive ion mode is presented, and some aspects of the ionization/desorption process leading to radical cations are studied.